1. Field of the Invention
The present invention relates generally to manufacture of heads for data storage devices and more specifically to a perpendicular write head for a hard disk drive.
2. Description of the Prior Art
Data has been conventionally stored in a thin media layer adjacent to the surface of a hard drive disk in a longitudinal mode, i.e., with the magnetic field of bits of stored information oriented generally along the direction of a circular data track, either in the same or opposite direction as that with which the disk moves relative to the transducer.
More recently, perpendicular magnetic recording systems have been developed for use in computer hard disk drives. A typical perpendicular recording head includes a trailing write pole, a leading return or opposing pole magnetically coupled to the write pole, and an electrically conductive magnetizing coil around the write pole. In this type of disk drive, the magnetic field of bits of stored information are oriented normal to the plane of the thin film of media, and thus perpendicular to the direction of a circular data track, hence the name.
Media used for perpendicular recording typically include a hard magnetic recording layer and a soft magnetic underlayer which provides a flux path from the trailing write pole to the leading opposing pole of the writer. Current is passed through the coil to create magnetic flux within the write pole. The magnetic flux passes from the write pole tip, through the hard magnetic recording track, into the soft underlayer, and across to the opposing pole, completing a loop of flux.
Perpendicular recording designs have the potential to support much higher linear densities than conventional longitudinal designs. Magnetization transitions on the bilayer recording disk are recorded by a trailing edge of the trailing pole and reproduce the shape of the trailing pole projection on the media plane, thus the size and shape of the pole tip is of crucial importance in determining the density of data that can be stored.
Perpendicular magnetic recording is expected to supersede longitudinal magnetic recording due to the ultra-high density magnetic recording that it enables. Increases in areal density have correspondingly required devising fabrication methods to substantially reduce the width of the P3 write pole tip while maintaining track-width control (TWC) and preserving trailing edge structural definition (TED). As mentioned above, the writing process reproduces the shape of the P3 write pole projection on the media plane, so the size of the P3 pole tip limits the size of the data fields and thus the areal density. The current drive is to make P3 pole tips of widths less than 200 nm (200×10−9 meters). Making reliable components of such microscopic size has been a challenge to the fabricating process arts. This problem is made even more challenging because the P3 pole tip shape at the ABS is preferably not a simple rectangle, but is trapezoidal, with parallel top and bottom edges, but a bevel angle preferably of approximately 6 to 15 degrees on the side edges. This is primarily done so that the P3 pole tip fits into the curved concentric tracks without the corners extending into an adjacent track by mistake. This is illustrated in FIGS. 5-7 (prior art). The width of the data track corresponds to the width of the P3 pole tip. In FIG. 5 (prior art) an un-beveled P3 pole tip 60 is shown on a first data track 6, with a second data track 7 adjacent to the first. The data tracks are actually curved, but at this scale, the curvature is so slight that it is represented as straight. It is not uncommon for the P3 pole tip 60 to become angled slightly as it follows the data track 6. FIG. 6 (prior art) shows the un-beveled P3 pole tip 60 which has been slightly tilted. It can be seen that although the upper corners of the un-beveled P3 pole tip 60 remain in the first track 6, the lower corner now intrudes into the adjacent track 7, which may contains previously written data, and which may now be distorted or partially written over by the intruding corner. As this tilting is common, it has become practice in the industry to bevel the P3 pole tip so that a trapezoidal shape is achieved, as shown in FIG. 7 (prior art). This produces what will be referred to as a beveled P3 pole tip 62. It can now be seen that the entire beveled P3 pole tip 62 is within the data track 6, despite the angle variation of the P3 pole tip 62 as a whole.
In fabrication of the beveled P3 pole tip, it is usual practice in the prior art to use an ion milling beam which is angled as shown by the ion milling direction arrow 9 in FIG. 8 (prior art) to shape the P3 pole tip 62, producing the bevel angle 3. However, it is difficult to control both the angle and the lateral positioning of the ion milling beam. As a result, the P3 pole tip 62 is not only beveled, but the milling process results in a reduction of the overall width of the P3 pole tip 62, as shown by the area in dashed lines that is lost in the process of producing the right hand bevel. The track width 5 is determined by the overall width of the P3 pole tip, as indicated by the arrow 5. This has the unintended effect of varying the track width 5 at the same time that the bevel angle 3 is produced. The problem is compounded when the left-hand side of the P3 pole tip 62 is also beveled, as shown in FIG. 9 (prior art), so that another area is lost and the overall width and thus the track width 5 is further reduced. To put this another way, in the processes of the prior art, the track width 5 and bevel angle 3 are not independently controlled. The eventual track width 5 depends on the control of the beam during the angular ion milling process, and there have traditionally been problems in maintaining satisfactory control over both of these variables simultaneously. This uncertainty of control results in poor yields as the track width dimension may easily be reduced too much below acceptable limits and thus the entire P3 pole tip structure must be discarded.
Thus there is a need for a method of production in which the bevel angle and track width produced are control as independent variables. There also is a need for a P3 pole tip that has at least one portion in which the width has been established independently of the bevel angle of the other portions of the P3 pole tip.